1. Field of the Invention
The present invention generally relates to an anti-thief security sensor assembly and, more particularly, to the anti-thief security sensor assembly that is used to form a part of a security system for detecting an intruder when he or she traverses across the path of travel of a detecting wave, for example, an infrared beam.
2. Description of the Prior Art
A security system of this kind is currently generally available in separate and integrated types. The separate type is of a structure in which a beam projecting unit and a beam receiving unit, each forming a security sensor assembly, are installed at opposite ends of a rectilinear guard area spaced an appropriate distance from each other with their optical axes aligned with each other; and the integrated type is of a structure in which, formed as a security sensor assembly, a pair of beam projecting and receiving units including respective sets of a beam projector and a beam receiver are installed at opposite sites to have their optical axes oriented towards a guard area. Regardless of the type, the security system now available in the art has a monitoring coverage ranging from a short rectilinear distance to a long rectilinear distance of, for example, a few hundred meters and generally requires the beam projector and the beam receiver to be optically accurately aligned with each other. In order for the optical axis between the beam projector and the beam receiver to be accurately adjusted, the security system is provided with a fine adjustment mechanism for adjusting one or both the horizontal angle and the vertical angle.
The fine adjustment mechanism hitherto employed in the anti-thief security system will be discussed in detail with reference to FIGS. 5A and 5B. As shown in FIG. 5A, an optical unit 50 having a downwardly extending working tongue 59 formed therewith, or otherwise rigidly secured thereto, is supported by two arms 52 of a generally U-shaped support frame 51 by means of respective coaxial support pins 53 so that the optical unit 50 can tilt about a common axis between the coaxial support pins 53. As shown in FIG. 5B, a torsion spring 54 is coiled around the support pin 53 and has its ends engaged with the adjacent arm 52 and a portion of the optical unit 50 to thereby urge the optical unit 50 in the direction indicated by the arrow P, that is, clockwise about the common axis between the support pins 53.
The support member 51 has a connecting base connecting the arms 52 together and having a stationary tongue 57 provided thereon so as to extend in a direction conforming to the direction in which the arms 52 extends. An adjustment screw 58 threadingly extends through an internally threaded hole defined in the stationary tongue 57 so as to terminate in abutment with the working tongue 59 rigid or integral with the optical unit 50. Since the optical unit 50 is urged in the clockwise direction P by the action of the torsion spring 54 as described above, the downwardly extending working tongue 59 is held in engagement with a tip of the adjustment screw 58 opposite to the screw head.
The conventional fine adjustment mechanism of the structure described above is of a design wherein as the adjustment screw 58 is turned to advance from a position shown by the phantom line, the tip of the adjustment screw 58 then held in engagement with the working tongue 59 pushes the working tongues 59 in a direction rearwardly, accompanied by turn of the optical unit 50 in a counterclockwise direction about the common axis between the support pins 53 as viewed in FIG. 5B. So to speak, turn of the adjustment screw 58 in a first direction results in the optical unit 50 being tilted against the resilient force of the torsion spring 54, but turn of the adjustment screw 58 in a second direction counter to the first direction allows the optical unit 50 to tilt as biased by the torsion spring 54. Thus, with the conventional fine adjustment mechanism, it is possible to adjust the angle of the optical unit in the vertical direction about the common axis between the support pins 53 in response to turn of the adjustment screw 58.
Adjustment of the angle of the optical unit in the vertical direction by means of the adjustment screw 58 for alignment of the optical axis is carried out while an attendant worker looks through view ports of a sighting device. For adjustment of the angle of the optical unit in the horizontal direction perpendicular to the vertical direction is often carried out by turning the support member 51 with hands in a right or left direction, which member 51 is rotatably mounted on a device body. It is to be noted that in the case the optical unit 50 discussed above is a beam projector, it includes a beam projecting element and at least one reflecting mirror or lens for reflecting infrared rays of light, projected from the projecting element, so as to project it as an infrared beam traveling in a predetermined direction, but where it is a beam receiver, it includes a beam receiving element and a reflecting mirror or condensing lens.
The conventional fine adjustment mechanism of the structure discussed above has a problem in that if the angle of tilt of the optical unit in the vertical direction is desired to be large, for example, within ±45° about the axis of tilt with respect to a reference position, the adjustment screw must have an increased length appropriate to the large angle of tilt of the optical unit. The use of the adjustment screw of the increased length results in increase in size, particularly the depth, of the housing structure and, in turn, results in unnecessary increase of the size of the anti-thief security device as a whole along with requirement to perform a job of adjustment of the optical axis for an increased length of time.
Also, considering that the adjustment screw 58 is so positioned that the attendant worker trying to perform the adjustment with a screwdriver is required to occupy a position in front of the optical unit 50 where the optical path of the optical unit 50 is defined. Accordingly, when the attendant worker attempts to performs a job of aligning the optical axis while looking through the view ports of the sighting device, one or both of the optical path traveling forwards from the optical unit and the field of view of the sighting device would be disturbed by his or her hands then manipulating the screwdriver, enough to make it difficult for the attendant worker to determine the orientation of the optical system and/or to determine the optimum tilt angle of the optical system that is generally done by monitoring the level of the incident infrared rays of light. For these reason, the attendant worker is often forced to take a labored attitude in such a way as to avoid his hand disturbing the path of travel of the infrared rays of light and/or the field of view of the sighting device while looking through the sighting device, thereby requiring a laborious work which in turn results in reduction in work efficiency.
In addition, since it is difficult to coordinate the operating direction for the angle adjustment, that is, the direction of turn of the adjustment screw 58 with the direction of tilt of the optical unit 50, the attendant worker often misapprehend the direction in which the adjustment screw 58 has to be turned, resulting in reduction in work efficiency as well. By way of example, when the optical unit 50 is desired to be tilted a certain angle in the clockwise direction P so that the optical unit 50 can be oriented upwards, it would be difficult to determine the direction in which the adjustment screw 58 has to be turned to turn the optical unit 50 in the clockwise direction P. In particular, considering that the beam projecting unit or the beam receiving unit now in use utilizes mostly a pair of optical units 50 positioned one above the other and in such case the optical units 50 are set in position having been tilted in respective directions opposite to each other, the adjustment screws 58 associated with the respective optical units 50 are required to be turned in respective directions opposite to each other so that the optical units 50 can be tilted in the directions opposite to each other. Accordingly, it is quite often that the attendant worker tends to misapprehend the respective directions in which the adjustment screws 58 have to be turned.